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单击以编辑,母版标题样式,单击以编辑母版文本样式,第二级,第三级,第四级,第五级,*,Prof.Jiakuan Yang,Huazhong University of Science and Technology,Air Pollution Control Engineering,Lecture,7-1,General ideas in air pollution control,Three alternatives for air pollution control,Air pollution control systems and equipment,Fluid velocities in air pollution control equipment,Minimizing volumetric flow rate and pressure drop,Efficiency,penetration,nines,Three alternatives for air pollution control,Improving the dispersion of our emission and thereby diluting the pollutants and lower the concentration near the ground level where people often exist.,Basic idea,Threshold value,(1)improve dispersion,The population density is 1 person/km,2,In a,sparely populated area,the pollutant emissions are eliminated by natural removal mechanisms and without causing any damage to the neighbors.,In a,densely populated world,dispersion is not a satisfactory approach.,For example,The population density is 29,000 persons/km,2,(Manhattan),(1)improve dispersion,(1)improve dispersion,Tall stack,the ground-level concentration,H,c,h,Problem,(1)improve dispersion,It will certainly decrease all the ground-level concentration near the stack,but it may increase some concentration far from stack with a tall stack.,SO,2,ultimately comes to ground,mostly with rain or snow for far away from the tall stack.,Raising the emission point of stack,may,raise the concentration far downwind,.,For example:,Acid-rain controversy,Tall stack,2001,年 度二 氧 化 硫 浓 度 区 域 分 布,2001,年 度 全 国 将 水,pH,值 分 布,(1)improve dispersion,Intermittent control schemes,Example 1,predictive control scheme,down wind,Stack,A fire-electric plant,morning exercise,6:30 8:00 A.M.,Opening center-park,(1)improve dispersion,h,T,Before 9:00 A.m.Shut off the production and stringent control of stack emission.,Temperature Inversion,Intermittent control schemes,(1)improve dispersion,Example 2,observation control system,Homes wood stoves:PM,10,Oxygenated motor fuels:CO,Intermittent control schemes,(1)improve dispersion,relocate the plant,The emission source should be far away from populated areas.Such as residential areas,commercial centers.,Reduce emission by process change,pollution prevention,water-based paints,Cleaner production,from raw material,old process,old technology,changed into a cleaner process,to prevent pollution.,Basic idea,Coal is replaced by natural gas as a home or business fuel.,(3)Use a downstream pollution control device,tailpipe,end-of the pipe control device,Designing air pollution control systems and equipment,Emission source,Hood,Blower,Control device,stack,Collected pollutant,Reduce emission,Resource recovery and ultimate fate of pollutants,Fluid velocities,Run cost,Efficiency,室内空气速度分布,18,（三）风压作用下的自然通风,风洞模型实验,20,风洞模型实验,21,A Typical continuous-feed mass-fired municipal Combustor,Resource recovery,If the pollutant is valuable material or a fuel,it may be more economical to collect and use it than to discard it.,Generally,reclamation or recovery is economical only if the concentrations are high enough in waste stream.,The ultimate fate of pollutants,Most particulate pollutant,e.g.fine dusts,to be captured and placed in a landfill.,Most organic compounds will burn.,Hazardous wastes disposal cost is higher.,Fluid velocities in air pollution control equipment,Minimize sum of pumping cost and capital cost of pipes and ducts.,Almost all industrial-sized flows of air or gases are turbulent.,40 to 60 ft/s(,12 to 18,m/s),Diameter,velocity,cost of pumping,Cost of the pipe,Minimizing volumetric flow rate and pressure drop,In the air pollution control system,fan or blower is the power source that propels the gas stream through the control device and the associated ductwork and exhaust stack.,Minimizing volumetric flow rate and pressure drop,n=molar flow rate,R=universal gas constant,T,1,=inlet absolute temperature,k=heat capacity ratio=1.4 for air and most waste gases,=fan or blower efficiency,P,1,=inlet absolute pressure of the fan,P,2,=outlet absolute pressure of the fan,Page 171,Minimizing volumetric flow rate and pressure drop,Q,Power,Efficiency,penetration,nines,Downstream control device,C,0,Q,1,C,1,Q,0,C,0,C,1,Q,0,C,0,Mass flow rate of contaminant into the device,Q,1,C,1,Mass flow rate of contaminant out of the device,Efficiency,penetration,nines,Efficiency,penetration,nines,99%,99.9%,90%,Efficiency,penetration,nines,Q,1,C,1,Q,3,C,3,Q,2,C,2,Q,0,C,0,Efficiency,penetration,nines,In the terms of penetration,Homogeneous and non-homogeneous pollutants,CO,SO,2,are homogeneous,Every CO molecule is identical to every other CO molecule.,Particles are not homogeneous,different particle with various sizes.,This Lecture and the Next Lecture,This Lecture:,Chapter 7 Page 160196,Page 202205,The Next Lecture:,Chapter 8 Page 209246,Exerciser,Page 203,7.5,Page 204,7.12,Page 205,7.19,7.21,DISCUSSION,Topics about Air pollution:,Introducing yourself,Interesting news or information about air pollution your,having read or heard,Your opinions
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